1. Field of the Invention
This invention relates to cellulosic substrates having improved wet strength and to a method for producing such substrates.
2. Description of the Prior Art
U.S. Pat. 2,834,675, issued May 13, 1958 discloses resinous compositions of dihaloalkanes and alkylene diamine which may be added to paper pulp to improve wet strength.
German Patent No. 955,835, published Jan. 10, 1957, discloses processes for water-proofing paper by adding to the pulp basic products free from reactive halogen or epoxy groups obtained by condensing polyamides with cross-linking compounds such as epichlorohydrin or dichloroethane. Such products also increase the wet strength of paper.
U.S. Pat. No. 2,595,935, issued May 6, 1952, discloses paper products of improved wet strength containing reaction products of alkylene diamine and bifunctional or polyfunctional halohydrins such as epichlorohydrin.
These prior art resinous compositions, although increasing wet strength, have other disadvantages which often makes them commercially unsatisfactory. For example, a resinous composition prepared by the reaction of dichloroethane and a alkylene diamine such as ethylenediamine is unsatisfactory in that it takes a long time to cure, in some instances, up to a year. It also is very inefficient, requiring appreciable amounts to obtain adequate wet strength. Likewise, one produced by reacting epichlorohydrin and a alkylene diamine such as hexamethylenediamine is less efficient.
Canadian Pat. No. 776,566 discloses wet and dry strength improvers obtained by reacting a polyamine having the formula EQU NH.sub.2 (Cm H.sub.2m NH).sub.p CmHm NH.sub.2
where m is an integer from 2 to 4 and p is an integer from 1 to 4 with an unbranched dihaloalkane of the formula X(CH.sub.2).sub.y X wherein X is a halogen and y is 2 or 3, and then reacting the amine prepolymer so formed with an epihalohydrin.
It has however, been found that such products have several grave disadvantages in that the amine prepolymers can only be prepared at low ratios of halogen equivalents to amine equivalents because at higher ratios, the product gels and is useless for further reaction. In addition, the further reaction with epihalohydrin is also restricted by the need to avoid gelation. In practice, this means less efficient use of the expensive amine and epihalohydrin components. Moreover, it is found that they are much inferior, as wet and dry strength resins, to the resins of the present invention.